Numerous contemporary medical procedures deliver drugs directly to target sites of diseased tissue. This targeted delivery has proven to be an advantageous approach for treating various medical conditions. Using targeted delivery, a controlled dose of the drug may be delivered directly to a target site while avoiding or minimizing exposing other parts of the body to the drug. Also, greater amounts of drug may be delivered to the afflicted parts of the body. In one approach to localized drug delivery, a balloon catheter is used, wherein the balloon has drug on its outer surface and is expanded within a vessel to deliver the drug to the vessel wall.
One problem often encountered with these techniques is inadequate drug release (or inadequate control thereof) when the balloon is deployed. For example, in conventional drug eluting balloons, much of the drug can be lost due to washing away by the flow of blood as the balloon is being delivered to the target site.
In an effort to avoid these problems, certain drug eluting balloon systems include a sheath disposed around a balloon. In one example, a sheath is provided around a balloon with one or more holes in the sheath for containing the drug. As the balloon is expanded, the sheath expands as well, causing the drug within the holes to be released to the target site.
Such systems have drawbacks, however. For example, much of the drug can remain in the holes even after expansion. As a result, very little drug is released. In some cases, as little as 10%-20% of the drug is released to the target site. To compensate for this, such drug eluting balloons have been provided with large amounts of excess medicament in order to ensure that a target site receives an adequate dose. In addition to this wastefulness, these devices also have poor control over the dosage of drug delivered to the target site.
An additional drawback of these systems is the potentially substantial loss of medicament as the balloon moves through the vasculature to the target site. The time it takes to guide the balloon through the system, which varies widely between patients, further compounds this problem. This variation adds to the difficulty in predicting the amount of medicament lost as the device travels to a target site. As a result, ensuring that the proper amount of medicament actually reaches the target site becomes problematic.
Accordingly, there is a need for a drug eluting system that more effectively releases a medicament to a target site.